One of the most basic things about leaves of all kinds, whether they’re on trees or plants, is that they make their own life-sustaining energy through the process of photosynthesis. Why can trees do this, but humans can’t? There are a few specific reasons, and one of the big ones is the presence of abiomolecule called chlorophyll, which is found in plants but not in humans. Not only is chlorophyll responsible for allowing plants to keep themselves going, but it’s also one of the biggest influences on the seasonal color changes that deciduous leaves experience.
The Life Cycle of a Pigment
Chlorophyll itself doesn’t change colors, so it’s only the starting point for explaining the mechanism behind the beautiful autumnal color change. If you look at chlorophyll molecules under a microscope, you’ll see that they’re uniformly green — bright green — and they stay that way throughout their lives. This is why leaves look green most of the time; chlorophyll acts as a pigment in addition to serving a part of the plant’s food factory.
In fact, chlorophyll absorbs the red and blue parts of the color spectrum, which is why it looks green. When chlorophyll is present in the leaf’s cells — which it is during spring and summer — the leaf looks green. But chlorophyll isn’t very stable, and it dies off quite easily. As temperatures get colder in the fall months, trees divert their nutrient resources away from leaves, which have evolved to be disposable specifically because resources become scarce in fall and winter. The chlorophyll begins to die off, setting the stage for a new color to appear on the leaves.
A New Pigment Steps Into the Spotlight
With chlorophyll moving out of the picture, other pigments in the leaves get the chance to shine. Different types of trees and plants have different pigments in addition to chlorophyll, which is why you see a rainbow of flamelike colors in the fall. Trees and plants that have a lot of carotene turn yellow, while those that have a lot of anthocyanins turn red. Factors such as temperature and sunshine have a further influence on what colors the leaves turn, but in the end, it all boils down to seasonal changes and pigment reactions.